I'm inclined to call that "optionally typed". As in, values nominally have a static type associated with them, but it's possible (even easy) to bypass the type

I'm inclined to call that "optionally typed". As in, values nominally have a static type associated with them, but it's possible (even easy) to bypass the type system. C#, for example, is mostly strong and static. But within 'unsafe' contexts you're allowed a lot of those kinds of C-style shenanigans, and you can replicate C unions using the StructLayout and FieldOffset attributes, so the type system is ultimately optional. I think of weak typing as a whole continuum of different things. At an extreme end you have C's level of optional typing. But there's also more tame stuff like implicit casting (which C# also has) that I'd also count as a form of weak typing.